Method and device for transmitting data unit

ABSTRACT

A method and a device for transmitting a data unit are disclosed. A method for transmitting a PPDU can comprise the steps of: generating, by an STA, the PPDU including a first portion and a second portion; and transmitting, by the STA, the PPDU, wherein the first portion is generated by performing IFFT according to a first FFT size, the second portion is generated by performing IFFT according to a second FFT size, and the first FFT size can differ from the second FFT size.

FIELD OF THE INVENTION

The present invention relates to wireless communications, and moreparticularly, to a method and a device for transmitting a data unit.

RELATED ART

A Wireless Next Generation Standing Committee (WNG SC) of institute ofelectrical and electronic engineers (IEEE) 802.11 is an AD-HOC committeethat a next-generation wireless local area network (WLAN) in the mediumand long term.

In an IEEE conference in March 2013, Broadcom presented the need ofdiscussion of the next-generation WLAN after IEEE 802.11ac in the firsthalf of 2013 when an IEEE 802.11ac standard is finished based on a WLANstandardization history. A motion for foundation of a study group whichOrange and Broadcom proposed in the IEEE conference in March 2013 andmost members agreed has been passed.

A scope of a high efficiency WLAN (HEW) which the next-generation WLANstudy group primarily discusses the next-generation study group calledthe HEW includes 1) improving a 802.11 physical (PHY) layer and a mediumaccess control (MAC) layer in bands of 2.4 GHz and 5 GHz, 2) increasingspectrum efficiency and area throughput, 3) improving performance inactual indoor and outdoor environments such as an environment in whichan interference source exists, a dense heterogeneous networkenvironment, and an environment in which a high user load exists, andthe like. That is, the HEW operates at 2.4 GHz and 5 GHz similarly tothe existing WLAN system. A primarily considered scenario is a denseenvironment in which access points (APs) and stations (STAs) are a lotand under such a situation, improvement of the spectrum efficiency andthe area throughput is discussed. In particular, in addition to theindoor environment, in the outdoor environment which is not considerablyconsidered in the existing WLAN, substantial performance improvement isconcerned.

In the HEW, scenarios such as wireless office, smart home, stadium,Hotspot, and building/apartment are largely concerned and discussionabout improvement of system performance in the dense environment inwhich the APs and the STAs are a lot is performed based on thecorresponding scenarios.

In the future, in the HEW, improvement of system performance in anoverlapping basic service set (OBSS) environment and improvement ofoutdoor environment performance, and cellular offloading are anticipatedto be actively discussed rather than improvement of single linkperformance in one basic service set (BSS). Directionality of the HEVmeans that the next-generation WLAN gradually has a technical scopesimilar to mobile communication. When a situation is considered, inwhich the mobile communication and the WLAN technology haven beendiscussed in a small cell and a direct-to-direct (D2D) communicationarea in recent years, technical and business convergence of thenext-generation WLAN and the mobile communication based on the HEW ispredicted to be further active.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide a method fortransmitting a physical layer convergence procedure (PLCP) protocol dataunit (PPDU).

Another aspect of the present invention is to provide a device fortransmitting a PPDU.

To achieve the foregoing aspects of the present invention, a method fortransmitting a physical layer convergence procedure (PLCP) protocol dataunit (PPDU) according to one embodiment of the present inventionincludes generating, by a station (STA), the PPDU including a firstportion and a second portion; and transmitting, by the STA, the PPDU,wherein the first portion is generated by performing an inverse fastFourier transform (IFFT) based on a first fast Fourier transform (FFT)size, the second portion is generated by performing an IFFT based on asecond FFT size, and the first FFT size is different from the secondFFT.

To achieve the foregoing aspects of the present invention, an STAtransmitting a PPDU in a wireless local area network (WLAN) according toanother embodiment of the present invention includes a radio frequency(RF) unit configured to transmit a radio signal and a processorselectively connected to the RF unit, wherein the processor isconfigured to generate the PPDU including a first portion and a secondportion and to transmit the PPDU, the first portion being generated byperforming an IFFT based on a first FFT size, the second portion beinggenerated by performing an IFFT based on a second FFT size, and thefirst FFT size being different from the second FFT.

Using a new-format physical layer convergence procedure (PLCP) protocoldata unit (PPDU) may minimize PLCP preamble overhead and providebackward compatibility for a legacy station (STA). Further, an STAsupporting a new-format PPDU may quickly determine whether a receivedPPDU is a new-format PPDU.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a concept view illustrating the structure of a wireless localarea network (WLAN).

FIG. 2 is a view illustrating a layer architecture of a WLAN systemsupported by IEEE 802.11.

FIG. 3 is a schematic view illustrating a broadband media access controltechnique in a wireless local area network (WLAN).

FIG. 4 is a schematic view illustrating a very high throughput (VHT)PPDU format in a WLAN.

FIG. 5 is a schematic view illustrating a PPDU transmitted through achannel.

FIG. 6 is a schematic view illustrating an HEW PPDU according to oneembodiment of the present invention.

FIG. 7 is a schematic view illustrating an HEW PPDU according to oneembodiment of the present invention.

FIG. 8 is a schematic view illustrating an HEW PPDU according to oneembodiment of the present invention.

FIG. 9 is a schematic view illustrating an HEW PPDU according to oneembodiment of the present invention.

FIG. 10 is a schematic view illustrating a subcarrier for transmittingan HEW PPDU according to one embodiment of the present invention.

FIG. 11 is a schematic view illustrating a method of an HEW STAdetecting an FFT size in an HEW PPDU according to one embodiment of thepresent invention.

FIG. 12 is a schematic view illustrating a method of an HEW STAdetecting an FFT size in an HEW PPDU according to one embodiment of thepresent invention.

FIG. 13 is a schematic view illustrating a method of an HEW STAdetecting an FFT size in an HEW PPDU according to one embodiment of thepresent invention.

FIG. 14 is a schematic view illustrating an operation when a legacy STAreceives an HEW PPDU according to one embodiment of the presentinvention.

FIG. 15 is a block diagram illustrating a wireless device to which anembodiment of the present invention may apply.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a concept view illustrating the structure of a wireless localarea network (WLAN).

An upper part of FIG. 1(A) shows the structure of the IEEE (institute ofelectrical and electronic engineers) 802.11 infrastructure network.

Referring to the upper part of FIG. 1(A), the WLAN system may includeone or more basic service sets (BSSs, 100 and 105). The BSS 100 or 105is a set of an AP such as AP (access point) 125 and an STA such as STA1(station) 100-1 that may successfully sync with each other tocommunicate with each other and is not the concept to indicate aparticular area. The BSS 105 may include one AP 130 and one or more STAs105-1 and 105-2 connectable to the AP 130.

The infrastructure BSS may include at least one STA, APs 125 and 130providing a distribution service, and a distribution system (DS) 110connecting multiple APs.

The distribution system 110 may implement an extended service set (ESS)140 by connecting a number of BSSs 100 and 105. The ESS 140 may be usedas a term to denote one network configured of one or more APs 125 and130 connected via the distribution system 110. The APs included in oneESS 140 may have the same SSID (service set identification).

The portal 120 may function as a bridge that performs connection of theWLAN network (IEEE 802.11) with other network (for example, 802.X).

In the infrastructure network as shown in the upper part of FIG. 1, anetwork between the APs 125 and 130 and a network between the APs 125and 130 and the STAs 100-1, 105-1, and 105-2 may be implemented.However, without the APs 125 and 130, a network may be establishedbetween the STAs to perform communication. The network that isestablished between the STAs without the APs 125 and 130 to performcommunication is defined as an ad-hoc network or an independent BSS(basic service set).

A lower part of FIG. 1 is a concept view illustrating an independentBSS.

Referring to the lower part of FIG. 1, the independent BSS (IBSS) is aBSS operating in ad-hoc mode. The IBSS does not include an AP, so thatit lacks a centralized management entity. In other words, in the IBSS,the STAs 150-1, 150-2, 150-3, 155-4 and 155-5 are managed in adistributed manner. In the IBSS, all of the STAs 150-1, 150-2, 150-3,155-4 and 155-5 may be mobile STAs, and access to the distributionsystem is not allowed so that the MSS forms a self-contained network.

The STA is some functional medium that includes a medium access control(MAC) following the IEEE (Institute of Electrical and ElectronicsEngineers) 802.11 standards and that includes a physical layer interfacefor radio media, and the term “STA” may, in its definition, include bothan AP and a non-AP STA (station).

The STA may be referred to by various terms such as mobile terminal,wireless device, wireless transmit/receive unit (WTRU), user equipment(UE), mobile station (MS), mobile subscriber unit, or simply referred toas a user.

FIG. 2 is a view illustrating a layer architecture of a WLAN systemsupported by IEEE 802.11.

FIG. 2 conceptually illustrates a layer architecture (PHY architecture)of a WLAN system.

The WLAN system layer architecture may include an MAC (medium accesscontrol) sub-layer 220, a PLCP (Physical Layer Convergence Procedure)sub-layer 210, and a PMD (Physical Medium Dependent) sub-layer 200. ThePLCP sub-layer 210 is implemented so that the MAC sub-layer 220 isoperated with the minimum dependency upon the PMD sub-layer 200. The PMDsub-layer 200 may serve as a transmission interface to communicate databetween a plurality of STAs.

The MAC sub-layer 220, the PLCP sub-layer 210, and the PMD sub-layer 200may conceptually include management entities.

The management entity of the MAC sub-layer 220 is denoted an MLME (MAClayer management entity, 225), and the management entity of the physicallayer is denoted a PLME (PHY layer management entity, 215). Suchmanagement entities may offer an interface where a layer managementoperation is conducted. The PLME 215 is connected with the MLME 225 tobe able to perform a management operation on the PLCP sub-layer 210 andthe PMD sub-layer 200, and the MLME 225 is also connected with the PLME215 to be able to perform a management operation on the MAC sub-layer220.

There may be an SME (STA management entity, 250) to perform a proper MAClayer operation. The SME 250 may be operated as a layer independentcomponent. The MLME, PLME, and SME may communicate information betweenthe mutual components based on primitive.

The operation of each sub-layer is briefly described below. The PLCPsub-layer 210 delivers an MPDU (MAC protocol data unit) received fromthe MAC sub-layer 220 according to an instruction from the MAC layerbetween the MAC sub-layer 220 and the PMD sub-layer 200 to the PMDsub-layer 200 or delivers a frame from the PMD sub-layer 200 to the MACsub-layer 220. The PMD sub-layer 200 is a PLCP sub-layer and the PMDsub-layer 200 may communicate data between a plurality of STAs by way ofa radio medium. The MPDU (MAC protocol data unit) delivered from the MACsub-layer 220 is denoted a PSDU (Physical Service Data Unit) on the sideof the PLCP sub-layer 210. The MPDU is similar to the PSDU, but in casean A-MPDU (aggregated MPDU), which is obtained by aggregating aplurality of MPDUs, has been delivered, each MPDUs may differ from thePSDU.

The PLCP sub-layer 210 adds an additional field including informationrequired by the physical layer transceiver while receiving the PSDU fromthe MAC sub-layer 220 and delivering the same to the PMD sub-layer 200.In this case, the added field may include a PLCP preamble to the PSDU, aPLCP header, and tail bits necessary to return the convolution encoderto zero state. The PLCP preamble may play a role to allow the receiverto prepare for syncing and antenna diversity before the PSDU istransmitted. The data field may include padding bits to the PSDU, aservice field including a bit sequence to initialize the scrambler, anda coded sequence in which a bit sequence added with tail bits has beenencoded. In this case, as the encoding scheme, one of BCC (BinaryConvolutional Coding) encoding or LDPC (Low Density Parity Check)encoding may be selected depending on the encoding scheme supported bythe STA receiving the PPDU. The PLCP header may include a fieldcontaining information on the PPDU (PLCP Protocol Data Unit) to betransmitted.

The PLCP sub-layer 210 adds the above-described fields to the PSDU togenerate the PPDU (PLCP Protocol Data Unit) and transmits the same to areceiving station via the PMD sub-layer 200, and the receiving stationreceives the PPDU and obtains information necessary for data restorationfrom the PLCP preamble and PLCP header to thus restore the same.

FIG. 3 is a schematic view illustrating a broadband media access controltechnique in a wireless local area network (WLAN).

WLAN standards preceding IEEE 802.11n support a 20 MHz channel bandwidthonly. IEEE 802.11n starts to support a 40 MHz channel bandwidth, andIEEE 802.11ac additionally supports 80 MHz and 160 MHz channelbandwidths.

FIG. 3 illustrates channel access in an 80 MHz channel bandwidthsupported by IEEE 802.11ac.

To coexist with existing IEEE 802.11b/g/n, IEEE 802.11ac can define a 20MHz channel for channel access based on distributed coordinationfunction (DCF) and enhanced distributed channel access (EDCA) protocols.The 20 MHz channel for channel access based on DCF and EDCA protocolsmay be referred to as a primary channel.

An STA may sense states of other channels than the primary channel 310in order to transmit a frame through a 40 MHz channel bandwidth or 80MHz channel bandwidth. The STA may sense the states of the channels(secondary channel 320, tertiary channel 330 and quaternary channel 340)other than the primary channel 310 for a certain period of time (forexample, PCF inter frame space (PIFS)) and determine a channel bandwidthfor transmitting data 350.

As a result, when all four 20 MHz channel bandwidths 310, 320, 330 and340 are available, the STA may transmit the data 350 through an 80 MHzbandwidths and receive a block acknowledgement (BA) through each 20 MHzchannel.

In IEEE 802.11ac, since an available channel bandwidth varies from 20MHz to 160 MHz, it is important to determine an appropriate channelbandwidth between a transmitting STA and a receiving STA in determiningperformance of a WLAN. IEEE 802.11ac may implement a dynamic channelbandwidth setting protocol based on a request to send (RTS) frame/clearto send (CTS) frame. According to the dynamic channel bandwidth settingprotocol, a transmitting STA may transmit an RTS frame through abroadband, and a receiving STA may transmit a CTS frame through acurrently available channel bandwidth. Specifically, a transmitting STAdesiring to use a 160 MHz channel bandwidth may transmit an RTS frame toa receiving STA through a 160 MHz channel bandwidth. When an 80 MHzchannel bandwidth is currently available, the receiving STA may transmita CTS frame to the transmitting STA through the 80 MHz channelbandwidth.

When the transmitting STA receives the CTS frame through the 80 MHzchannel bandwidth, the transmitting STA may transmit data to thereceiving STA through a channel bandwidth smaller than the 80 MHzchannel bandwidth used for receiving the CTS frame.

FIG. 4 is a schematic view illustrating a very high throughput (VHT)PPDU format in a WLAN.

FIG. 4 discloses a VHT PPDU defined in IEEE 802.11ac.

For compatibility with a legacy STA, the VHT PPDU may include alegacy-short training field (L-STF) 400, a legacy-long training field(L-LTF) 410, and a legacy signal field (L-SIG) 420.

The L-STF 400 may include an L-STF sequence. The L-STF sequence may beused for frame detection, automatic gain control (AGC), diversitydetection and coarse frequency/time synchronization.

The L-LTF 410 may include an L-LTF sequence. The L-LTF sequence may beused for fine frequency/time synchronization and channel prediction.

The L-SIG 420 may include control information. Specifically, the L-SIG420 may include information on data rate and data length.

A VHT-SIG-A 430 may include information for interpreting the VHT PPDU.The VHT-SIG-A 430 may include a VHT-SIG-A1 and a VHT-SIG-A2. TheVHT-SIG-A1 may include bandwidth information on a used channel, whetherspace-time block coding is applied, a group identifier (ID) indicatinggrouped STAs for multi-user (MU)-multiple-input and multiple-output(MIMO) and information on the number of space-time streams used forimplementing MU-MIMO. The bandwidth information on the channel includedin the VHT-SIG-A1 may include information on a bandwidth used fortransmitting a field followed by the VHT-SIG-A1.

The VHT-SIG-A2 may include information on whether a short guard interval(GI) is used, forward error correction (FEC) information, information ona modulation and coding scheme (MCS) for a single user, information onchannel coding types for multiple users, beamforming relatedinformation, redundancy bits for cyclic redundancy checking (CRC) andtail bits of a convolutional decoder.

A VHT-STF 440 may be used to improve automatic gain control (AGC)estimation in an MIMO environment.

A VHT-LTF 450 is used for channel estimation in an MIMO environment.

A VHT-SIG-B 460 may include information on each STA, that is,information on PSDU length and a MCS, tail bits or the like.

A Data 470 is a payload, which may include a SERVICE field, a scrambledPLCP service data unit (PSDU), tail bits and padding bits.

FIG. 5 is a schematic view illustrating a PPDU transmitted through achannel.

FIG. 5 discloses a PPDU format for MU-MIMO.

FIG. 5 discloses space-time streams transmitted by an AP inMU-MIMO-based communications between the AP and two STAs (first STA andsecond STA).

Among four space-time streams 510, 520, 530 and 540, two space-timestreams 510 and 520 may be allocated to transmit data to a first STA,and the remaining two space-time streams 530 and 540 may be allocated totransmit data to a second STA. Each space-time stream may be transmittedthrough a 20 MHz channel bandwidth. The respective space-time streamsmay be referred to as a first space-time stream 510 to a fourthspace-time stream 540, and channels for transmitting the firstspace-time stream 510 to the fourth space-time stream 540 may bereferred to as a first channel to a fourth channel.

Referring to FIG. 5, among fields transmitted respectively through thefirst space-time stream 510 to the fourth space-time stream 540, anL-STF, L-LTF, L-SIG and VHT-SIG-A may be duplicated. That is, the L-STF,L-LTF, L-SIG and VHT-SIG-A transmitted respectively through a pluralityof 20 MHz channel bandwidths may be duplicated fields.

A field followed by the VHT-SIG-A 550 in each space-time streamtransmitted through 20 MHz may include different information dependingon a space-time stream. Enhanced features, such as MIMO, MU-MIMO andtransmission through an extended channel bandwidth, may be applied tothe field followed by the VHT-SIG-A 550.

The VHT-SIG-A 550 may include information on a bandwidth for atransmitting STA to transmit data and information on the number ofspace-time streams allocated to respective receiving STAs. A receivingSTA may determine a channel bandwidth for receiving data transmittedafter the VHT-SIG-A 550 based on the information on the bandwidthtransmitted through the VHT-SIG-A 550. When the information on thebandwidth is not transmitted through the VHT-SIG-A 550, the receivingSTA performs blind detection for a bandwidth available for transmissionto retrieve a bandwidth for transmitting data.

Further, in MU-MIMO, the receiving STA may determine a data stream toreceive based on space-time stream allocation information included inthe VHT-SIG-A 550.

In detail, the VHT-SIG-A 550 may include the bandwidth information,which indicates 80 MHz for transmitting data, and the information on thenumber of the space-time streams allocated to the respective receivingSTAs, which indicates that the first STA is allocated the two space-timestreams 510 and 520 and the second STA is allocated the two space-timestreams 530 and 540.

The first STA and the second STA may receive data from the transmittingSTA based on the information included in the VHT-SIG-A 550.

Next, one embodiment of the present invention discloses a PPDU formatfor a next-generation WLAN after IEEE802.11ac to satisfy a demand forhigh throughput and quality of experience (QoE) performance improvement.

Hereinafter, for convenience of description, a next-generation WLAN maybe referred to as a high efficiency WLAN (HEW), a frame supporting theHEW as an HEW frame, a PPDU supporting the HEW as an HEW PPDU, and anSTA supporting the HEW as an HEW STA.

In addition, a PPDU other than an HEW PPDU, such as a non-HT PPDU, HTPPDU or VHT PPDU, may be referred to as a legacy PPDU, a frametransmitted and received through a legacy PPDU as a legacy frame, and anSTA supporting only a legacy PPDU as a legacy STA. These terms arearbitrary terms which may be replaced with a variety of different terms.

When an HEW PPDU is used in the HEW, the HEW PPDU may be used totransmit and receive data in an environment where the HEW PPDU coexistswith a legacy PPDU for legacy STAs supporting an existing WLAN system.In this environment, the legacy STAs may have no backward compatibilitywith the HEW. Thus, the HEW PPDU needs to be defined so as not to affectthe legacy STAs. That is, the HEW PPDU needs to minimize overhead of aPCLP preamble and simultaneously support legacy STAs.

For convenience, the HEW PPDU may be divided into a legacy part to anL-SIG and an HEW part followed by the L-SIG. For example, the HEW partmay include at least one of fields for supporting the HEW, such asHEW-SIG-A, HEW-STF, HEW-LTF and HEW-SIG-B. These fields for supportingthe HEW are illustrative fields for interpreting the HEW PPDU excludingthe legacy part. Specifically, an HEW-SIG-A, HEW-SIG-B and HEW-SIG-ABare illustrative signaling fields including information for decoding theHEW part, and an HEW-STF and HEW-LTF(s) are illustrative training fieldsused for AGC and/or channel prediction and channel/frequency tracking inthe HEW part.

FIG. 6 is a schematic view illustrating an HEW PPDU according to oneembodiment of the present invention.

Referring to FIG. 6, an HEW part of the HEW PPDU may sequentiallyinclude an HEW-SIG-A 610, an HEW-STF 620, an HEW-LTF(s) 630 and anHEW-SIG-B 640. For convenience of description, a Data field is assumedto be included in the HEW part.

The HEW-SIG-A 610 is a first signaling field of the HEW part. TheHEW-SIG-A 610 may include channel bandwidth information. The channelbandwidth information may indicate the size of a channel bandwidth usedfor transmitting fields included in the HEW part followed by theHEW-SIG-A 610 (for example, HEW-STF 620, HEW-LTF(s) 630, HEW-SIG-B 640and Data field 650). A receiving STA which receives the HEW PPDU mayreceive data included in a field transmitted after the HEW-SIG-A 610through a channel bandwidth indicated by the channel bandwidthinformation. When the receiving STA does not recognize the channelbandwidth information, the receiving STA needs to detect the size of achannel bandwidth for the HEW part after the HEW-SIG-A 610 based onblind detection. Further, the HEW-SIG-A 610 may include additionalinformation for decoding the HEW PPDU.

The HEW-STF 620 may be used for AGC of data transmitted after theHEW-STF 620 in the HEW PPDU.

The HEW-LTF(s) 630 may be used for channel prediction for decoding theHEW-SIG-B 640 and/or Data field 650. The number of HEW-LTFs 630 may bedetermined based on the number of space-time streams.

The HEW-SIG-B 640 may be used to provide necessary information forsupporting downlink (DL)/uplink (UL) MU-MIMO or to transmit additionalinformation for supporting the HEW.

The HEW-SIG-A, HEW-SIG-B or HEW-SIG-A/B may include the following piecesof information for supporting the HEW. The HEW-SIG-A, HEW-SIG-B orHEW-SIG-AB may be referred to as an HEW signaling field.

The HEW is capable of supporting OFDMA in a multiple access mode, andthe HEW signaling fields may include information for supporting multipleaccess. For example, the HEW signaling fields may include information ona frequency band (or channel) allocated to each of a plurality of STAs.Identifier (ID) information, such as group identifier (GID) of each STA,may be used to indicate a frequency band allocated to each of the STAs,and the HEW signaling fields may indicate information on a usedfrequency band for an STA based on the GID of the STA.

In addition, the HEW may support UL-MIMO, and the HEW signaling fieldsmay include information on whether UL-MIMO is allowed, information onthe number of space-time streams used in UL-MIMO, and information on achannel used for UL-MIMO.

Alternatively, the HEW allows an AP and a plurality of STAs tosimultaneously perform communications and allows the AP to transmitinformation on STAs to simultaneously transmit and receive data. The HEWsignaling fields may include information on the number of STAs acquiringthe same transmission opportunity (TXOP) or a list of STAs acquiring thesame TXOP. Also, the HEW signaling fields may transmit information onthe duration of the TXOP.

FIG. 7 is a schematic view illustrating an HEW PPDU according to oneembodiment of the present invention.

Referring to FIG. 7, an HEW part of the HEW PPDU may sequentiallyinclude an HEW-STF 710, an HEW-LTF(s) 720 and an HEW-SIG-AB 730.

In the HEW PPDU, the HEW-STF 710 may precede a signaling field (forexample, HEW-SIG-AB 730). As described above, when there is no channelbandwidth information for the HEW part transmitted through the signalingfield, a receiving STA needs to detect the size of a channel bandwidthfor the HEW part based on blind detection. Thus, in the HEW PPDUaccording to the embodiment of the present invention, to avoid blinddetection, a sequence constituting the HEW-STF 710 (HEW-STF sequence)may include the channel bandwidth information for the HEW part. TheHEW-STF sequence may be allocated to a plurality of subcarriers on anOFDM symbol (HEW-STF OFDM symbol) transmitting the HEW-STF 710.

Different HEW-STF sequences may indicate the sizes of different channelbandwidths for the HEW part. That is, a particular HEW-STF sequence mayindicate the size of a particular channel bandwidth allocated to the HEWpart.

According to another embodiment of the present invention, when thechannel bandwidth for the HEW part is determined on a channel bandwidthindicated in a legacy part, the HEW-STF sequence may include no channelbandwidth information.

According to still another embodiment of the present invention, theHEW-STF sequence may include not only channel bandwidth information butinformation on a guard interval (GI) or cyclic prefix (CP) of an OFDMsymbol used for transmitting the HEW part. Hereinafter, in theembodiment of the present invention, the GI and the CP may beinterpreted as having the same meaning and the term “GI” is used forconvenience of description.

In the HEW, various lengths of GIs (long GI, double GI and triple GI)may be used depending on wireless communication environments. TheHEW-STF sequence may include the information on the GI of the OFDMsymbol used for transmitting the HEW part.

In the HEW, the length of a GI for the HEW PPDU may vary depending oncommunication environments, and the HEW-STF sequence may includeinformation on the length of a used GI. In the HEW, an HEW PPDUoptimized according to the length of a GI may be used. That is, the HEWPPDU may be configurable depending on the length of the GI.

The HEW-STF sequence may independently transmit the channel bandwidthinformation and the GI information but transmit information on acombination of the channel bandwidth information and the GI information.For example, a first HEW-STF sequence may indicate a first channelbandwidth size and a first GI length, and a second HEW-STF sequence mayindicate a first channel bandwidth size and a second GI length.

Alternatively, the receiving STA may roughly determine size informationon a fast Fourier transform (FFT) based on a signal waveform of theHEW-STF sequence to estimate channel bandwidth information. Theestimated channel bandwidth information may be identified based on thechannel bandwidth information included in the HEW-SIG-AB 730 transmittedafter the HEW-STF 710.

The HEW-LTF(s) 720 may be used for channel estimation for decoding theHEW-SIG-AB 730 and/or Data field 740. The number of HEW-LTF(s) 720included in the HEW PPDU may be determined based on the number ofspace-time streams.

FIG. 8 is a schematic view illustrating an HEW PPDU according to oneembodiment of the present invention.

Referring to FIG. 8, an HEW part of the HEW PPDU may sequentiallyinclude an HEW-STF 810 and an HEW-SIG-AB 820.

The HEW PPDU may include no HEW-LTF. Instead of the HEW-LTF, theHEW-SIG-AB 820 and a Data field 850 may each include a signal forchannel prediction (for example, pilot signal) to perform channelprediction. The signal for channel prediction may be used not only forchannel prediction but also for channel tracking and/or frequencytracking.

According to another embodiment of the present invention, when the HEWPPDU is sufficiently transmitted within a coherence time due toinsignificant changes in an channel environment, an L-LTF 840 includedin a legacy part may be used for decoding the HEW part. In detail, achannel prediction result predicted based on the L-LTF 840 may be usedfor decoding the HEW part.

FIG. 9 is a schematic view illustrating an HEW PPDU according to oneembodiment of the present invention.

Referring to FIG. 9, an HEW part of the HEW PPDU may include anHEW-SIG-A/B 910 only.

The HEW PPDU may include no HEW-STF. Thus, an L-STF 930 of a legacy partmay be used for AGC of the HEW part. Specifically, when quantizationlevel ranges of analog-to-digital converter (ADC) terminals are notsignificantly different in the legacy part and the HEW part, the HEWpart includes no HEW-STF and the L-STF 930 may be used for AGC of theHEW part.

As described above in FIG. 8, the HEW PPDU may include no HEW-LTF. Asdescribed above, instead of the HEW-LTF, the HEW-SIG-A/B 910 and a Datafield 920 may each include a signal for channel prediction (for example,pilot signal) to perform channel prediction. Alternatively, an L-LTF 940included in the legacy part may be used for decoding the HEW part.

According to the embodiment of the present invention, a transmitting STAwhich transmits the HEW PPDU may periodically transmit an HEW PPDUincluding an HEW-STF and/or HEW-LTF.

The HEW-STF and HEW-LTF periodically transmitted through the HEW PPDUmay be designed in a minimal structure intensively considering asynchronization function. Information on a transmission period of theHEW-STF and HEW-LTF is system information, which may be transmitted asincluded in a frame used for initial channel access (for example, atleast one frame of a beacon frame, probe response frame and associationresponse frame).

FIG. 10 is a schematic view illustrating a subcarrier for transmittingan HEW PPDU according to one embodiment of the present invention.

Referring to FIG. 10, a legacy part 1000 and an HEW part 1050 of the HEWPPDU may be generated based on different FFT sizes. FIG. 10 illustratesFFT size changes of the legacy part 1000 and the HEW part 1050 withreference to the HEW PPDU illustrated in FIG. 6. The HEW part 1050 isassumed to include a Data field.

In an outdoor WLAN communication environment, a delay spread mayincrease. To reduce effects of the increase in delay spread, an FFT witha different size from that for the legacy part 1000 may be applied tothe HEW part.

Specifically, a 64-FFT may be applied to the legacy part 1000 in a 20MHz channel bandwidth. 52 subcarriers based on the 64-FFT may be used totransmit data, among which 48 subcarriers may be used to transmittraffic data and four subcarriers to etransmit a pilot signal. Aninterval between subcarriers may be 312.5 kHz. Further, the size (orwidth) of an OFDM symbol may be a 4 usec, and the length of a GI (TGI)may be 0.8 usec. The size of an active (or useful, vaild, available)OFDM symbol may be 3.2 usec, which is obtained by subtracting the TGI(0.8 usec) from the size of the OFDM symbol (4 usec).

According to the embodiment of the present invention, a 128-FFT may beapplied to the HEW part 1050 in a 20 MHz channel bandwidth.

When the 128-FFT is used, 104 subcarriers based on the 128-FFT may beused for data transmission. When the 104 subcarriers are used, aninterval between subcarriers may be 312.5/2 (=156.25) kHz. The intervalbetween subcarriers may be the inverse number of the width of an activeOFDM symbol obtained by subtracting a TGI from the size of an OFDMsymbol. Thus, when the 104 subcarriers are used, the size of the activeOFDM symbol may increase to 6.4 usec, which is twice as long as 3.2 usecand the TGI may also be increased to 1.6 usec, which is twice as long as0.8 usec. That is, the length of the OFDM symbol may be increased from 4usec to 8 usec. According to the embodiment of the present invention,the length of the TGI may be adjusted depending on communicationenvironments. When the TGI has a length of 0.8 usec, the length of theactive OFDM symbol is increased to 7.2 usec and data throughput per unittime (or unit symbol) may increase. Using an FFT with an increased sizemay increase the TGI and accordingly increase transmission coverage ofthe HEW PPDU.

Application of FFTs with different sizes may be described as follows inview of generation of a PPDU by an STA.

An STA may generate and transmit a PPDU including a first portion(legacy part or L-SIG) and a second portion (HEW part, HEW-SIC-A orHEW-SIG-AB). The first portion may be generated by performing an inverseFFT (IFFT) based on a first FFT size, and the second portion may begenerated by performing an IFFT based on a second FFT size. Here, thefirst FFT size may be different from the second FFT, and the second FFTsize may be a multiple of 2 times as large as the first FFT size.

It may be assumed that the first portion is transmitted on a first OFDMsymbol and the second portion is transmitted on a second OFDM symbol. Inthis case, the duration of the first OFDM symbol may be the sum of afirst guard interval duration and a first FFT period determined on thefirst FFT size, and the duration of the second OFDM symbol may be thesum of a second guard interval duration and a second FFT perioddetermined on the second FFT size. Here, the second guard intervalduration may be longer than the first guard interval duration.

The 128-FFT is an example of an FFT with an increased size, and a256-FFT and 512-FFT may also be used, which are included in anembodiment within the scope of the present invention. Using an FFT withan increased size may increase transmission coverage of the HEW PPDU.

When the FFT size for the legacy part 1000 and the HEW part 1050 aredifferent as above, a problem may occur when the STA decodes a PPDU dueto application of OFDM numerology to the legacy part 1000 and the HEWpart 1050 in different manners.

An HEW STA needs to be able to decode both the legacy part 1000 and theHEW part 1050. Thus, the HEW STA needs to detect portions of the HEWPPDU subjected to FFTs with different sizes. Detecting portions of anHEW PPDU subjected to FFTs with different sizes may also be referred toas an OFDM numerology check.

When there are portions subjected to FFTs with different sizes (forexample, a multiple of 2 times, for example, four times) in a receivedPPDU, the HEW STA may determine the received PPDU as an HEW PPDU. On thecontrary, when there are portions subjected to FFTs with different sizesin a received PPDU after the legacy part (L-STF, L-LTF and L-SIG) 1000,a legacy STA may determine the received PPDU as an HEW PPDU and notperform additional decoding.

Hereinafter, one embodiment of the present invention discloses a methodof an HEW STA detecting portions subjected to FFTs with different sizesin an HEW PPDU.

FIG. 11 is a schematic view illustrating a method of an HEW STAdetecting an FFT size in an HEW PPDU according to one embodiment of thepresent invention.

Referring to FIG. 11, an HEW STA may determine an FFT size applied to aguard interval period 1150 of an OFDM symbol allocated to a field (atemporally first field in an HEW part in an HEW PPDU) followed by alegacy part (L-STF, L-LTF and L-SIG) 1100 of a received PPDU. That is,the HEW STA may determine an FFT size used for a channel bandwidth givenin the guard interval period 1150 of the OFDM symbol allocated to thefield followed by the legacy part 1100. As a result of determination,when the FFT size is changed, the HEW STA may determine the receivedPPDU as an HEW PPDU.

The number of subcarriers on an OFDM symbol corresponding to the HEWpart may be a multiple of 2 times (for example, twice, four times andthe like) as large as the number of subcarriers on an OFDM symbolcorresponding to the legacy part.

According to the embodiment of the present invention, to determine achange in FFT size by an STA, some OFDM symbols allocated for the HEWpart in the HEW PPDU may include a GI with a sufficient length. Forexample, the GI for some OFDM symbols allocated for the HEW part may bea long GI, a double GI or a triple GI. For example, the double GI has alength twice as long as the short GI, and the triple GI has a lengththree times as long as the short GI.

FIG. 12 is a schematic view illustrating a method of an HEW STAdetecting an FFT size in an HEW PPDU according to one embodiment of thepresent invention.

FIG. 12 discloses a configuration of a GI of an HEW part in the HEWPPDU.

In FIG. 12, it is assumed that as an illustrative example of an HEWPPDU, an HEW part of an HEW PPDU includes an HEW-SIG-A, HEW-STF,HEW-LTF, HEW-SIG-B and Data field as illustrated in FIG. 6. Further, itis assumed that the HEW-SIG-A is allocated two OFDM symbols.

In this case, the OFDM symbols for the HEW-SIG-A as a first field of theHEW part may include a long GI, double GI or triple GI.

As illustrated at the top of FIG. 12, when a plurality of OFDM symbolsis allocated to the HEW-SIG-A 1200, a long GI 1250 may be included ineach OFDM symbol corresponding to the HEW-SIG-A 1200.

Alternatively, as illustrated at the bottom of FIG. 12, to facilitatedetermination of an FFT size change by the HEW STA, a first OFDM symbol1280 among the OFDM symbols allocated to the HEW-SIG-A 1270 may includea double GI 1290 or triple GI, and the other OFDM 1285 may include arelatively shorter GI or no GI.

FIG. 13 is a schematic view illustrating a method of an HEW STAdetecting an FFT size in an HEW PPDU according to one embodiment of thepresent invention.

FIG. 13 discloses an FFT size detection method of the HEW STA when atraining field, such as HEW-STF (or HEW-LTF), is located as a firstfield of an HEW part.

For example, the HEW STA may detect a sequence correlation of an OFDMsymbol transmitted subsequent to a legacy part 1300 (hereinafter,“detection OFDM symbol 1350).

When the sequence correlation of the detection OFDM symbol 1350 isdetermined as a first correlation characteristic, the HEW STA maydetermine the FFT size as a first FFT size. When the sequencecorrelation of the detection OFDM symbol 1350 is determined as a secondcorrelation characteristic, the HEW STA may determine the FFT size as asecond FFT size. When the FFT size is determined as the second FFT size,the HEW STA may determine the OFDM symbol transmitted subsequent to thelegacy part 1300 as an HEW-STF included in the HEW part.

As described above, when the HEW-STF precedes a signaling field (forexample, HEW-SIG-A), the HEW STA may need to perform blind detection inan OFDM symbol corresponding to the HEW-STF in order to acquire channelbandwidth information. To solve such a problem, an HEW-STF sequence maybe mapped onto channel bandwidth information, and the HEW STA mayacquire the channel bandwidth information based on the HEW-STF sequence.

For example, when the HEW PPDU includes an HEW-STF, HEW-LTF, HEW-SIG-ABand Data field, an HEW-STF sequence may include channel bandwidthinformation and the HEW-SIG may include no separate channel bandwidthinformation.

FIG. 14 is a schematic view illustrating an operation when a legacy STAreceives an HEW PPDU according to one embodiment of the presentinvention.

FIG. 14 is described with reference to the HEW PPDU illustrated in FIG.6.

Referring to FIG. 14, the legacy STA detects a field followed by alegacy part 1400 (field followed by an L-SIG). When the field is a fieldnot decodable (for example, a field generated based on a different FFTsize), the legacy STA may configure a network allocation vector (NAV)based on a length field in the L-SIG without performing additionaldecoding and defer channel access.

That is, as different OFDM numerologies are applied to the legacy part1400 and an HEW part 1450, the legacy STA may determine the HEW part1450 as a field not decodable.

Alternatively, the legacy STA may determine constellation information onup to at least one OFDM symbol followed by the legacy part 1400 usingauto-detection rules in order to determine whether a received PPDU is adecodable PPDU format. That is, the legacy STA may determine whether thereceived PPDU is a decodable PPDU format based on the constellationinformation on the at least one OFDM symbol followed by the legacy part.

FIG. 15 is a block diagram illustrating a wireless device to which anembodiment of the present invention may apply.

Referring to FIG. 15, the wireless device may be an STA that mayimplement the above-described embodiments, and the wireless device maybe an AP 1500 or a non-AP STA (or STA)(1550).

The AP 1500 includes a processor 1510, a memory 1520, and an RF (RadioFrequency) unit 1530.

The RF unit 1530 may be connected with the processor 1510 totransmit/receive radio signals.

The processor 1510 implements functions, processes, and/or methods asproposed herein. For example, the processor 1510 may be implemented toperform the operation of the above-described wireless device accordingto an embodiment disclosed in FIG. 6 to FIG. 14 of the presentinvention.

For example, the processor 1510 may be configured to generate andtransmit a PPDU including a first portion and a second portion. Thefirst portion may be generated by performing an inverse FFT (IFFT) basedon a first FFT size, and the second portion may be generated byperforming an IFFT based on a second FFT size.

The STA 1550 includes a processor 1560, a memory 1570, and an RF (RadioFrequency) unit 1580.

The RF unit 1580 may be connected with the processor 1560 totransmit/receive radio signals.

The processor 1560 implements functions, processes, and/or methods asproposed herein. For example, the processor 1560 may be implemented toperform the operation of the above-described wireless device accordingto an embodiment disclosed in FIG. 6 to FIG. 14 of the presentinvention.

For example, the processor 1560 may be configured to determine an HEWpart in a received PPDU based on a change in FFT size used in thereceived PPDU.

The processor 1510, 1560 may include an ASIC (Application-SpecificIntegrated Circuit), other chipset, a logic circuit, a data processingdevice, and/or a converter that performs conversion between a basebandsignal and a radio signal. The memory 1520, 1570 may include a ROM(Read-Only Memory), a RAM (Random Access Memory), a flash memory, amemory card, a storage medium, and/or other storage device. The RF unit1530, 1580 may include one or more antennas that transmit and/or receiveradio signals.

When an embodiment is implemented in software, the above-describedschemes may be embodied in modules (processes, or functions, etc.)performing the above-described functions. The modules may be stored inthe memory 1520, 1570 and may be executed by the processor 1610, 1660.The memory 1520, 1570 may be positioned in or outside the processor1610, 1660 and may be connected with the processor 1510, 1560 viavarious well-known means.

What is claimed is:
 1. A method for transmitting a physical layerconvergence procedure (PLCP) protocol data unit (PPDU) the methodcomprising: generating, by a station (STA) (1500, 1550), the PPDUincluding a legacy part and a High Efficiency Wireless (HEW) part; andtransmitting, by the STA (1500, 1550), the PPDU, wherein the legacy partis generated by performing an inverse fast Fourier transform, (IFFT) ina given channel bandwidth based on a first fast Fourier transform (FFT)size, wherein the HEW part is generated by performing an IFFT in thegiven channel bandwidth based on a second FFT size, and wherein thefirst FFT size is different from the second FFT size.
 2. The method ofclaim 1, wherein the legacy part is transmitted on a first orthogonalfrequency division multiplexing (OFDM) symbol, wherein the HEW part istransmitted on a second OFDM symbol, wherein a duration of the firstOFDM symbol is a sum of a first guard interval duration and a first FFTperiod determined on the first FFT size, and wherein a duration of thesecond OFDM symbol is a sum of a second guard interval duration and asecond FFT period determined on the second FFT size.
 3. The method ofclaim 2, wherein the second guard interval duration is longer than thefirst guard interval duration.
 4. The method of claim 2, wherein anumber of subcarriers in the second OFDM symbol is larger than a numberof subcarriers in the first OFDM symbol.
 5. The method of claim 1,wherein the second FFT size is larger than the first FFT size.
 6. Astation (STA) transmitting a physical layer convergence procedure (PLCP)protocol data unit (PPDU) the STA (1500, 1550) comprising: a radiofrequency (RF) unit (1530, 1580) configured to transmit a radio signal;and a processor (1510, 1560) operatively connected to the RF unit (1530,1580) and configured to: generate the PPDU comprising a legacy part anda High Efficiency Wireless (HEW) part; and transmit the PPDU, whereinthe legacy part is generated by performing an inverse fast Fouriertransform, (IFFT) in a given channel bandwidth based on a first fastFourier transform (FFT) size, wherein the HEW part is generated byperforming an IFFT in the given channel bandwidth based on a second FFTsize, and the first FFT size is different from the second FFT size. 7.The STA of claim 6, wherein the legacy part is transmitted on a firstorthogonal frequency division multiplexing (OFDM) symbol, wherein theHEW part is transmitted on a second OFDM symbol, wherein a duration ofthe first OFDM symbol is a sum of a first guard interval duration and afirst FFT period determined on the first FFT size, and wherein aduration of the second OFDM symbol is a sum of a second guard intervalduration and a second FFT period determined on the second FFT size. 8.The STA of claim 7, wherein the second guard interval duration is longerthan the first guard interval duration.
 9. The STA of claim 7, wherein anumber of subcarriers in the second OFDM symbol is larger than a numberof subcarriers in the first OFDM symbol.
 10. The STA of claim 6, whereinthe second FFT size is larger than the first FFT size.